The present invention relates to an agent for preventing scale formation and a method for preventing scale formation. More particularly, the present invention relates to an agent for preventing scale formation and a method for the same which is effective in preventing scale formation in water systems, such as cooling water systems, boiler water systems, and the like. The present invention is particularly effective in preventing calcium and silicate scale formation.
Scale obstructions are generated on heat exchange surfaces and inside pipes which are in contact with water in a water system, such as a cooling water system, a boiler water system, or the like. The types of scales which are deposited include calcium carbonate, calcium sulfate, calcium sulfite, calcium phosphate, calcium silicate, magnesium silicate, magnesium hydroxide, zinc phosphate, zinc hydroxide, basic zinc carbonate, and the like. Scale formation is particularly troublesome in water systems that employ high concentration operation. In, for example, an open circulating cooling water system, high concentration operation is preferred to conserve resources and energy. However, when a high concentration operation is performed by reducing the amount of cooling water blow to the outside of the system, dissolved salts become concentrated in the water. In addition to the heat exchange surfaces becoming more likely to corrode, the solubility of the dissolved salts declines, resulting in scale formation. The resulting scale obstructions can become major impediments to the operation of boilers or heat exchange devices by reducing heat transfer efficiency and by narrowing pipes.
Polymers which contain carboxyl groups, such as polymerized maleic acid, acrylic acid, itaconic acid, and the like are often effective in inhibiting formation of calcium or magnesium scale. Furthermore, copolymers which combine monomers with a carboxyl group and monomers which contain a sulfonic acid group, such as vinyl sulfonic acid, allyl sulfonic acid, and 2-acrylamide-2-methylpropane sulfonic acid, are often used as scale preventing agents, depending on the water quality. To inhibit formation of silica scale, scale preventing agents such as acrylamide polymers, cation polymers, polyethylene glycol, and the like, have been proposed. Thus, different polymers have been used to inhibit scale formation, depending on the type of scale. However, to date no universal scale formation preventing agent has been described.
The water used in water systems is typically industrial water or tap water. These types of waters contain numerous and various ions. Particularly when conducting high concentration operations in a cooling water system or a boiler water system, for example, there is a need for a scale preventing agent which can effectively respond to all scale types. Currently, there is no scale preventing agent which satisfies this requirement. Of particular concern is the fact that there is no scale preventing agent which effectively prevents the adhesion of silica scale.
In Japanese Laid Open Patent Publication Number 61-107998, there is proposed a scale preventing agent which has an excellent effect in preventing silica scale formation. The scale preventing agent proposed in this publication contains acrylamide polymer and acrylic acid polymer. When the silica concentration is low, acrylamide polymer has a good scale preventing effect. However, when the silica concentration is high, the effect is reduced. In Japanese Laid Open Patent Publication Number 7-256266, there is disclosed a water treatment method in which a water soluble cationic polymer, halogenated aliphatic nitro alcohol, a low molecular weight carboxylic acid polymer, or phosphonic acid are added. However, because the proposed cation polymer is a quaternary ammonium salt, the cationic property is extremely strong. Under these conditions, the components of the water treatment method can form gel reaction products with silica. Furthermore, slime from microorganisms can also form easily. As a result, the use of the proposed water soluble cationic polymer is disadvantageous, because of problems arising from the clogging of pipes.
In Japanese Laid Open Patent Publication Number 2-31894, a scale preventing agent containing polyethylene glycol and a low molecular weight carboxylic acid polymer or phosphonic acid is proposed. However, although polyethylene glycol is effective in controlling the adherence of scale when the silica concentration is low, it is easily influenced by other ions, and the effect is not stable.